This invention relates in general to electroplating metals on a conductive substrate and, more particularly, to an apparatus for brush plating of workpieces.
Forming metal layers on conductive substrates has long been accomplished by electroplating. In conventional electroplating, the object to be plated (the cathode) and an anode are suspended in an electrolyte that contains salts of the metal to be deposited and often other chemicals to assist in the electrochemical action. The anode is connected to the positive pole of a direct current source, such as a battery, and the object or cathode is connected to the negative pole. The anode may be formed from the metal being plated or from an inert conductor, such as platinum. Metal from the electrolyte is deposited in a uniform coating on the object being plated. If the anode is inert, the electrolyte must be regularly replenished with the metal being deposited.
Electroplating is used for many purposes, such as the plating protective, hard, metal surfaces on softer metal substrates, the production of jewelry by plating precious metals on base metal substrates and the repair of worn metal objects, such as bearings and the like, by deposition additional metal in worn areas.
In some cases it is necessary to plate portions of objects that are too large to be conveniently placed entirely in a plating bath, or where only a small portion of the object is to be plated. Typically, a bearing on a long rotating shaft, bearing journals on electric motor shafts and the like require repair when worn to the point where excessive play and vibration occurs between the shaft and bearing. Often the diameter of the shaft has worn to the point that it is 0.0005 to 0.002 inch undersize, so that electroplating of a uniform thin, adherent layer of the shaft metal around the shaft is necessary.
Brush plating was developed to permit such localized plating. In its simplest form, brush plating can be accomplished with an ordinary paint brush, with a small piece of metal adjacent to one side of the bristles to act as the anode. The brush anode and the object to be plated are connected to a direct current source, the brush is dipped in the electrolyte and the brush is moved across the surface to be plated. With repeated dipping and brushing, an electroplated layer will be built up on the object surface.
While effective with small areas and limited thickness plating, this prior art system of brush plating has a number of problems. Cleaning of the object to be plated must be done separately. Electrocleaning, where a reverse current and an electrolyte is used to remove a small amount of metal from the object surface, is difficult to accomplish and will often contaminate the brush. Plating is very slow, with the need to constantly dip the brush in the electrolyte. In some cases, a squirt bottle can be used to replenish the brush electrolyte. The brush and squirt bottle, if used, will tend to drip or splatter electrolyte, especially where a slowly rotating shaft surface is to be plated. Some of the plating solutions are quite costly, so wasted solution can be a considerable expense. Where cleaning solutions and various activator etchant solutions are used to obtain improved plating, the process must stop between steps to allow the object to be rinsed with water to remove the previous solution and prevent contamination. Either different brushes must be used for the different solutions or a single brush must be cleaned carefully between solutions.
While brush plating has applications in some small, light plating, applications, these problems prevent brush plating from being effectively used in the repair of structural objects where high quality plating to uniform thicknesses without contamination on a rapid, production line basis is required.
Thus, there is a continuing need for improved brush plating systems allowing rapid plating to relatively thick layers on a rapid basis while avoiding contamination between different solutions used in the plating operation.